Drainage question

[NeilTheSpectacular]

Hi. New forum member here.

I am in the process of adapting our garage to house a washing machine and possibly a small sink.

I will be digging a trench across the garden for the necessary services (electric, cold water and drainage).

I'm happy with the required depths for each of the services. Planning to put water at around 900mm, drainage at around 750mm and then electric around 600mm (correct me if this is incorrect).

Mostly its straight forward, but I'm struggling to get a consistent and correct answer regarding the drainage.

Questions are...

Given its purely washing machine and sink waste. Do I need the run from the garage to the combined sewer pipe to be fitted with access points?

Currently planning to fit a branch into a straight section of clay pipe between 2 man holes (inspection chambers are concrete and only have inlet/outlets so I can't attach to these).

Is it ok to connect waste water drainage into an existing drain pipe in this way? I can't see another way to do it.

I've had a ground worker look at it and he was just going to cut into the existing pipe and bury it all. No access points until it gets into the garage!
Any help/assistance would be much appreciated.

 

[Hugh Jaleak]

Water only needs to be 760mm (3 ft) deep for frost protection purposes, 900mm is overkill. Drainage needs to be determined by depth of existing sewer, then work back looking at a 1:40 fall (gradient) on the pipework. Electric, deep enough to avoid an accidental damage by someone being over zealous with a spade in the future. Warning tape for Buried Services underneath is never a bad idea.

Basic rule of drainage is, all pipework must be accessible for rodding in the event of a blockage. Whilst the proposed new section will only carry water, should the run it couples onto, block, and then this lateral run fill with sewage, then it is conceivable that it could block as a side effect of the first blockage. (Often find with blockages, the water still manages to seep away, leaving a plug of congealed solid matter behind, which gradually increases and adds to the issue.)

A blind connection into an existing run is not usually an issue, provided there is access for rodding/jetting form the other end of the run. You can break into a concrete chamber if need be, but its a fair bit of work. However, if the depth of the existing drain is not ridiculous, and it's not in the middle of a driveway etc, then I'd just fit a 450mm plastic chamber where you break into the existing sewer and be done with it. Assuming a straight run to the garage, the other end can have direct connection to the drain if required, or trapped gulley, whichever is easiest.

Yes, this is the correct and only method to be getting rid of waste water, it must go to a foul sewer.

 

[NeilTheSpectacular]

Thanks for the reply. Very helpful!

I may revise the depths then but as you say the depths of the drainage will potentially govern the rest of the depths.

Ideally the point of of connection is actually fairly close to the concrete chamber (probably about 1mtr downstream of it) so was hoping to avoid adding a further chamber at the point of connection so we didn't end up with 2 man holes in close proximity in the garden.

I did wonder if it would be sufficient to rod it from within the garage. Effectively I was thinking to have a short stack in the corner of the garage, through the floor slab and then a long radius bend beneath the slab which connects to the run across to the main sewer. Not sure if this would work? Rodding access to the main is good with man holes either end of the point id join up to.

The other question is the termination of the stack within the garage. Can this just be capped off or would I need the stack to be vented?

Thanks for your help! I have been reading the building regs but it doesn't quite seem clear on this specific query.

 

[Ian H]

You could start with a small stack or gully with access.

Most important thing is making sure your man makes 2 good joints on the new junction he fits.